1. Field of the Invention
The invention involves both processes and devices which employ flexible substrates made from a material impregnated with a resin of a particular composition.
2. Description of the Prior Art
The use of flexible substrates for the manufacture of electronic devices is growing rapidly. Flexible substrates are particularly advantageous where rapid, low-cost manufacturing is desirable. Particularly attractive is the possibility of using continuous fabrication techniques with rolls of flexible substrate.
The difficulties in obtaining suitable flexible substrates are formidable. The reason for this is the extensive combination of properties which are required to obtain satisfactory electronic devices using flexible substrates. For example, the flexible dielectric substrate should be suitable for bonding to copper, should be dimensionally stable and have long-term thermal stability. In addition, the flexible dielectric material should be suitable for soldering, have reasonable cost and good mechanical strength. Also required is high tear strength, low cold flow, and low water absorption. Other required properties are high fire retardivity, good punchability and availability in continuous rolls. Most important of all are its electrical properties. It should have good insulator properties such as high resistance and low dissipative losses, and high breakdown voltage. Although many such materials have been proposed and used, improvements in some or all of the properties described above is highly desirable. Much background material on flexible circuitry is given in an article by J. M. Rausch in Electronic Packaging and Production 15 (5); 91 (1975).